1. Field of the Invention
The present invention relates to an ink for ink jet, and an ink cartridge and an ink jet recording method using the ink.
2. Description of the Related Art
According to an ink jet recording method, recording can be made on various recording media. Various inks such as, for example, an ink suitable for recording an image of photograph-like image quality on glossy paper and an ink suitable for recording documents on plain paper have been proposed according to purposes thereof for recording a better image. In recent years, the ink jet recording method has been utilized even in recording of business documents including characters and graphic charts using plain paper as a recording medium, and the frequency of use in such use applications markedly increases. Therefore, the use of pigments as coloring materials for not only a black ink but also color inks as inks suitable for recording characters and graphic charts on a recording medium such as plain paper increases.
Under such circumstances, various investigations on a monoazo pigment among pigments used in inks for ink jet are advanced because the pigment is excellent in coloring ability and advantageous even from the viewpoint of cost. However, the monoazo pigment is generally weak against heat, so that the following problem is caused when the monoazo pigment is applied to an ink jet system in which an ink is ejected from a recording head by the action of thermal energy. For example, it is known that when C.I. Pigment Yellow 74 that is a representative monoazo pigment is used, a precipitate of the pigment adheres to and deposits in the interior of an ink flow path of a recording head to lower ejection properties. In particular, in recent years, there has been an increasing demand for more improving the number of pages recordable and lowering a running cost. There has thus been a strong demand for inhibiting the lowering of ejection properties at a level higher than before.
In order to solve such a problem, the following proposals have been made. It has been proposed to inhibit lowering of ejection stability and storage stability of an ink by containing a substance capable of inhibiting aggregation of a monoazo pigment dispersed by a resin dispersant in the ink and improve the color developability of the resulting image (see Japanese Patent Application Laid-Open No. 2006-225638). In addition, there has been proposed an ink containing a monoazo pigment of a self-dispersible type in which a hydrophilic group has been bonded to the surface of a pigment particle, a water-soluble organic compound and a substance for inhibiting aggregation of the monoazo pigment (see Japanese Patent Application Laid-Open No. 2006-199744). This ink is said to inhibit lowering of ejection stability and storage stability even in an ink jet system utilizing thermal energy and enable improving the color developability of the resulting image.